Transfer of photoenergy in pi-conjugated polymers. Two types of photoluminescence that involve energy transfer along a polymer chain

Two types of energy transfer in pi-conjugated polymers have been investigated using time-resolved photoluminescence (PL) techniques: type i, perpendicular-type energy transfer from the 2,3-di(p-tolyl)quinoxaline unit to the pi-conjugated main chain of poly[2,3-di(p-tolyl)quinoxaline-5,8-diyl], and type ii, parallel-type energy transfer from the oligo(pyridine-2,5-diyl) (O-Py) unit to the oligo(selenophene-2,5-diyl) (O-Se) unit in a block-type copolymer of O-Py and O-Se. Both types of energy transfer were very fast with a time constant shorter than approximately 0.1 ns; in particular, the type ii energy transfer took place with a time constant of approximately 5 ps. Both pi-conjugated polymers were considered to contain segments with various effective pi-conjugation lengths, and the energy transfer to the segment with a larger effective pi-conjugation length and a smaller pi-pi* transition energy required a longer transition time. A polarizing film was obtained by utilizing the perpendicular-type energy transfer.     

Molecular dynamics study of thermal phenomena in an ultrathin liquid film sheared between solid surfaces: the influence of the crystal plane on energy and momentum transfer at solid-liquid interfaces

A molecular dynamics study has been performed on a liquid film sheared between moving solid walls. Thermal phenomena that occur in the Couette-like flow were examined, including energy conversion from macroscopic flow energy to thermal energy, i.e., viscous heating in the macroscopic sense, and heat conduction from the liquid film to the solid wall via liquid-solid interfaces. Four types of crystal planes of fcc lattice were assumed for the surface of the solid wall. The jumps in velocity and temperature at the interface resulting from deteriorated transfer characteristics of thermal energy and momentum at the interface were observed. It was found that the transfer characteristics of thermal energy and momentum at the interfaces are greatly influenced by the types of crystal plane of the solid wall surface which contacts the liquid film. The mechanism by which such a molecular scale structure influences the energy transfer at the interface was examined by analyzing the molecular motion and its contribution to energy transfer at the solid-liquid interface.     

Influence of environment induced correlated fluctuations in electronic coupling on coherent excitation energy transfer dynamics in model photosynthetic systems

Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light harvesting complex, we explore the influence of including correlations in inter-chromophore couplings between different chromophore dimers that share a common chromophore. We find that the relative sign of the different correlations can have profound influence on decoherence time and energy transfer rate and can provide sensitive control of relaxation in these complex quantum dynamical open systems.     

煤显微组分分子结构模型的量子化学研究

采用分子力学和半经验量子化学方法，研究了神木煤显微组分的分子结构模型，比较了镜质组和惰质组分子模型的能量构成、不同类型键的键长和键裂解能。研究结果表明，扭转能和范德华能是分子中的主要作用力，取代基对体系能量有明显影响，烷基取代基使体系能量增加，而苯基取代基使体系能量降低；脂肪C—C键长比芳香C—C键长长，说明脂肪C—C在受热过程中比芳香C—C更容易断裂分解。对各键裂解能的计算结果表明，Car—Cal键的裂解能高于Cal—Cal，Car—O醚键的裂解能高于Cal—O醚键。而惰质组结构模型中除C—O醚键外，各键的裂解能均高于镜质组，说明惰质组结构模型比镜质组有较高的热稳定性。     

聚合物系统中的传能和光化学

评论了聚合物系统中非辐射能量传递类型,影响能量传递的因素,以及能量传递同聚合物光化学的关系,附22篇文献。     

Analyzing Reaction Rates with the Distortion/Interaction‐Activation Strain Model

The activation strain or distortion/interaction model is a tool to analyze activation barriers that determine reaction rates. For bimolecular reactions, the activation energies are the sum of the energies to distort the reactants into geometries they have in transition states plus the interaction energies between the two distorted molecules. The energy required to distort the molecules is called the activation strain or distortion energy. This energy is the principal contributor to the activation barrier. The transition state occurs when this activation strain is overcome by the stabilizing interaction energy. Following the changes in these energies along the reaction coordinate gives insights into the factors controlling reactivity. This model has been applied to reactions of all types in both organic and inorganic chemistry, including substitutions and eliminations, cycloadditions, and several types of organometallic reactions.     

Construction of divergent anthracene arrays within dendritic frameworks

This publication presents simple methodologies for construction of divergent anthracene arrays either within structural interior or at peripheral positions of dendritic frameworks. The synthetic approaches employed multiple coupling reactions between two types of 10-functionalized 9-anthryl chlorides and two types of polyphenolic linkers, resulting in four types of dendritic architectures. Successful implementation of the syntheses was confirmed by a range of spectroscopies along with elemental analyses and size exclusion chromatography studies. The resulting dendritic molecules showed a range of solubilities in chloroform fairly affected by the dendritic backbone structures. Fluorescence spectroscopic experiments of the multichromophoric dendritic systems indicated pronounced energy delocalization functionalities via an energy migration within the branched molecular frameworks as expressed in reduced fluorescence quantum yields and complex emission decay profiles.     

Density functional theory and molecular clusters

Density functional theory (DFT) methods, including nonlocal density gradient terms in the exchange and correlation energy functionals, were applied to various types of molecular clusters: H-bonded, ionic, electrostatic, and London. Reliable results on the structure and stabilization energy were obtained for the first two types of cluster as long as Becke3LYP and Becke3P86 functionals and basis sets of at least DZ + P quality were used. DFT methods with currently available functionals failed completely, however, for London-type clusters, for which no minimum was found on the potential energy surfaces. DFT interaction energy exhibits the same basis set extension dependence as the Hartree-Fock (HF) interaction energy. Therefore, the Boys-Bernardi function counterpoise procedure should be employed for elimination of the DFT basis set superposition error. © 1995 John Wiley & Sons, Inc.     

Caractérisation par émission acoustique de l’adhérence et de l’endommagement d’un revêtement : cas d’un revêtement WC–Co sur acier

This note presents a characterization method of the ‘adhesion’ of a coating by acoustic emission technique. In situ acoustic emission measurements which were investigated in terms of amplitude, absolute energy, position of the event, etc. were performed on WC–Co coated specimens prepared by HVOF (high velocity oxy fuel) during four-point bending tests. The microscopic observations of the specimens show two types of cracks: transversal cracks (regularly spaced on the coating surface) and interfacial cracks. Acoustic emission results show two different types of acoustic events in terms of absolute energy and amplitude, which are representative of two cracking mechanisms.     

Quantitative evaluation of interference reactions in photon activation analysis

Interferences of different types (competing reactions, overlapping photons emission energies etc.) occur more frequently during activation analysis with high energy exciting radiation that in conventional thermal neutron activation. Three main types of interference in high energy photon activation analysis (PAA) have been determined quantitatively, using experimentally obtained data exclusively. Based on the results presented, it is possible in many critical cases to improve significantly the accuracy of analysis results obtained by PAA.     

Internal rotation and rotational isomerism in substituted ethanes

The types of potential energy curves of internal rotation in substituted ethanes were studied. Formulas for the calculation of the energy differences in rotational isomers and of the potential barriers to internal rotation in these derivatives were obtained by Bernstein's method. As a rule, the calculated results are in agreement with experiment.     

Theoretical investigation of excited states of molecules. An application on the nitrogen molecule

Diverse existing lines for the calculation of excited states are exposed, with an emphasis on those methods that consider both types of correlation energy: the dynamic and the non-dynamic one. We analyze the possibility of to calculate the dynamic correlation energy using a correlation energy density functional applied to a multi-determinantal wavefunction, which would include the non-dynamic correlation energy, versus the use of mono-determinantal wavefunctions, which are not able to include the long-range correlation energy, and versus the use of variational or perturbative calculations from multi-determinantal wavefunctions, with their excessive computational cost. The results obtained with several methods are compared. Contribution to the Serafin Fraga Memorial Issue.     

Élaboration de nouvelles lois de comportement pour les élastomères : principe et avantages

A phenomenological study of deformed rubber in uniaxial tension, pure shear and equi-biaxial tension, leads to a generalized strain energy density representation for hyperelastic elastomeric material behaviour. A strain energy density function family is built with a new process. It is particularly well adapted for representing experimental data of different types of loading, and so, for a wide class of elastomers. Besides, parameter identification of this family of strain energy density functions is simple and fast.     

《光电化学及新型太阳能电池》专辑序言

众所周知,能源与环境是当今人类面临的最大难题和挑战,随着世界能源需求的急剧攀升,传统化石资源的不断耗竭,全球温室效应和环境污染的压力日趋严重,发展各种可再生绿色能源成为当今世界最主要的共性问题和研究热点. 太阳能光电转化技术被认为是一种最有希望真正解决未来社会可再生能源和洁净环境问题的先进技术. 太阳可为人类提供取之不尽、用之不竭的巨大能源宝库,每年照射到地球的太阳能量高达174000TW,换言之,只要能以10%效率转化0.1%到达地球表面的太阳能,即可满足全球的能源需求. 当前国际上最热点研究的新型太阳能电池包括染料敏化太阳能电池、有机太阳能电池、量子点太阳能电池及钙钛矿太阳能电池等,这些新型太阳能电池的研究近年来取得了长足的进步,世界上每年发表相关论文超过10000篇,其中中国学者在太阳能光电化学理论、光电转化器件设计、电极材料、有机半导体光伏材料、电解质系统、有机及钙钛矿太阳能电池电极界面修饰层材料等方面开展了大量卓有特色的工作,为推进各种新型太阳能电池的进步和应用做出不菲的贡献. 光电化学是一门研究光与电化学相互作用的交叉学科,是太阳能高效利用中光-电转化和光能-化学能转化的核心理论基础. 自上世纪70年代以来,光电化学理论得到不断发展和完善,为当今蓬勃发展的各种新型太阳能电池和光催化制氢等提供了强有力的理论指导. 然而,随着纳米科技、材料科学及半导体物理等现代科技的飞速发展和多学科深入研究,诸多新型太阳能体系研究的新现象和复杂性仍未能得到圆满解析. 仍亟需进一步从微观水平认识太阳能电化学电池及光电催化的反应本质,发展原位表征和超快时间分辨技术研究光生电子的传输、复合及界面反应等规律及定量关系,为人们设计高光电转化效率的电化学太阳能电池、推进商品化应用提供理论指导. 本专辑围绕光电化学及新型太阳能电池专题,收录了在相关研究领域具有丰富积累和影响的团队所撰写的9篇相关研究进展的综述文章和研究论文,部分反映了我国在新型太阳能电池结构设计、合成方法和性能研究方面的研究进展.希望借助该专刊的出版,能使广大读者更深入地了解我国在新型太阳能电池领域的研究现状、研究趋势和存在的问题及挑战,推动我国光电化学及新型太阳能电池研究的进一步发展. 在此,对本专辑的所有作者、审稿人及编辑部工作人员的卓有成效的工作和付出表示衷心的感谢！     

Recent advances in multifunctional electrochromic energy storage devices and photoelectrochromic devices

Multifunctional devices integrated with electrochromism and energy storage or energy production functions are attractive because these devices can be used as an effective approach to address the energy crisis and environmental pollution in society today. In this review, we explain the operation principles of electrochromic energy storage devices including electrochromic supercapacitors, electrochromic batteries, and the photoelectrochromic devices. Furthermore, the material candidates and structure types of these multifunctional devices are discussed in detail. The major challenges of these devices along with a further outlook are highlighted at the end.     

On the quality of basis sets

An analysis of the quality of a given basis set is presented in terms of the three fundamental parts of total energy. This analysis clearly displays three types of error occasionally present in the components of total energy. As an illustration of the application of these concepts, several STO and Gaussian basis sets for the Ni atom are analyzed.     

Nanotubular boron-carbon heterojunctions

Linear nanotubular boron-carbon heterojunctions are systematically constructed and studied with the help of ab initio total energy calculations. The structural compatibility of the two classes of materials is shown, and a simple recipe that determines all types of stable linear junctions is illustrated in some detail. Our results also suggest the compatibility of various technologically interesting types of nanotubular materials, leading to different types of nanotubular compound materials, and pointing out the possibility of wiring nanotubular devices within heterogeneous nanotubular networks.     

Crystal orbital studies of polymers with defects

The ab-initio SCF crystal orbital method is used to describe the energy bands in polymers with defects. It is shown that defects of the bond length types have pronounced effects on energy gaps between valence and conduction bands.     

人工光合作用

人工光合作用是模拟自然界的光合作用过程,设计制备人工光催化体系,以达到高效吸收、转化和储存太阳能的目的。本文从自然界的光合作用过程出发,综述了国内外人工光合作用的最新研究进展。从基本原理、常用体系和能量转换效率等方面入手,系统介绍了两种人工光合作用体系:模拟自然光合作用系统的超分子和无机半导体光催化体系。在此基础上,分析当前研究中存在的问题,并提出改进能量转换效率的可能对策,最后评述了人工光合作用的发展趋势和应用前景。